This invention relates to the art of manufacturing parts from metallic sheet material using hot metal forming dies and more particularly to new and improved constructions and techniques for producing metal parts featuring the rapid and trouble-free extraction of formed parts from hot working surfaces of superplastic and quick plastic forming dies.
Prior to the present invention, various types of forming equipment and processes have been developed to form sheets of alloys of aluminum and other suitable metallic materials into a wide range of items such as sturdy and lightweight panels for vehicles. Among such equipment and processes are superplastic and quick plastic forming dies and processes in which a ductile sheet of suitable metallic material is heated and stretched onto the forming surfaces of heated dies to improve production of high quality parts. Examples of such processes and equipment are found in U.S. Pat. No. 5,974,847 issued Nov. 2, 1999 to Saunders et al for xe2x80x9cSuperplastic Forming Processxe2x80x9d and U.S. Pat. No. 5,819,572 issued Oct. 13, 1998 to Krajewski for xe2x80x9cLubricating System for Hot Formingxe2x80x9d, both assigned to the assignee of this invention and both hereby incorporated by reference. In the patent to Saunders et al, a sheet of metal alloy is heated to a superplastic forming temperature and is pulled over and around a forming insert prior to using differential gas pressure to further stretch the sheet into conformity with a forming die surface so that thinning of the formed part is minimized. In the patent to Krajewski, dry lubricant is applied to metallic sheets which are subsequently heated to predetermined forming temperatures and formed into a part in superplastic forming die equipment. The lubricant initially provides improved forming of the part and subsequently improved release of the formed part from the forming die.
While such hot plastic forming processes and equipment generate improved parts, production efficiency has at times been diminished because of rejection of blemished or damaged parts produced by production procedures. Often such damage results from mechanical damage occurring from the physical removal of the formed part from the hot forming surface of the die and subsequently from the handling of the hot part. More particularly, after the part has been initially separated from the hot forming die, the part retains sufficient heat energy causing the surfaces thereof to retain some plasticity so that the tooling and handling marks may be imposed on the part from removal and stacking equipment.
Moreover, initial removal has heretofore been difficult because the formed part often firmly seats or grips on the die-forming surface. Dislodgment of such parts by extraction forces exerted through release tooling often results in part distortion or part marring by the tools or dies. This damage may be so substantial that parts do not meet specifications and have to be scrapped and recycled. The use of larger quantities of lubricants to improve parting requires more frequent and excessive die cleaning between forming operations and provides only minimized improvement in part removal. Often the lubricant remaining on the dies caused part imperfection on the show surfaces as pointed out in U.S. Ser. No. 09/748,096 filed Dec. 27, 2000 by Morales et al, entitled xe2x80x9cHot Die Cleaning for Superplastic and Quick Plastic Formingxe2x80x9d and assigned to the assignee of this invention and hereby incorporated by reference.
In contrast to the prior art, the present invention is drawn to new and improved methods and mechanisms that provide improved parts and meets higher standards for ejection and removal of formed parts from hot superplastic and quick plastic forming dies while in the press and operating at elevated temperatures. More particularly, the invention is directed to the quick and effective removal of formed parts from hot forming dies without part damage and with optimized usage of parting lubricants.
This invention provides new and improved equipment and method for unseating the formed part from the heated die. In a preferred embodiment of this invention, a series of orificed air passages or jets extending through the forming surface of the die are employed to direct streams of compressed air between the die surface and the formed part. The pressurized air is effective at the interface between the forming surface and the formed part to provide an outwardly directed force, urging the formed part away from the forming surface of the heated die. The air passing through the jet orifices may accumulate between the formed part and the die surface to effectively reduce the amount of static friction that must be overcome in separating the two components.
Release air may also flow to the periphery of the formed part to break any sealing or loosen the seating between the part and the forming die to augment part release. Additionally, the air that passes through the orifices effectively cools the formed panel, which contracts at a high rate due to its high coefficient of thermal expansion and high surface area-to-mass ratio as compared to that of the die unit with its lower coefficient of thermal expansion and lower surface area-to-mass ratio. Since the die does not contract the same amount as the formed part, the difference in contraction reduces the area of intimate contact between the panel and the die surface, thereby reducing the amount of static friction that must be overcome in separating these two components from one another.
The above factors all contribute to the lowering of the force required to separate the formed panel from the die. This reduction in force allows the formed part to be removed from the hot die without damage and with minimum effort and distortion. Moreover, since the panel has been cooled by the air streams, its plasticity is reduced and can be quickly handled with removal and stacking equipment with minimized damage. With improved part extraction, parting lubricant usage can be reduced for improved production efficiency and effective cost reduction.
These and other features, objects and advantages will become more apparent from the following detailed description and drawings in which: